A base station transceiver is one of important components of a mobile communication network. The function of the transmitter part of the base station transceiver is to convert a signal that is modulated and carries information into a high-power radio-frequency signal, which is transmitted through a subsequent antenna. The base station transceiver is developing towards smaller volume, lower power consumption and higher communication speed.
In the base station transceiver, a power amplifier (briefly referred to as PA), as one of core components, functions to amplify a signal to a sufficient power level, so as to achieve transmission, long-distance transport and reliable reception of the signal. In the power consumption of the whole base station transceiver, the power consumption of the power amplifier accounts for 40%, and the working efficiency of the power amplifier is generally 30% to 40%, therefore, how to improve the working efficiency of the power amplifier while ensuring the linearity of the power amplifier is a research focus of the industry.
FIG. 1 is a schematic structural diagram of a transmitter in the prior art. In FIG. 1, a baseband data modulator 101 modulates a digital signal to be sent into a specific waveform signal which meets radio frequency transmission requirements; and the specific waveform signal is converted into an actual analog waveform signal through a digital-to-analog converter (DAC) 103. As the working frequency of the digital-to-analog converter is low, the frequency of the output signal generally cannot meet requirements of the frequency band of the transmitter, and therefore, an intermediate-frequency signal which has low frequency and is output by the digital-to-analog converter is further modulated onto a carrier frequency through a mixer 105 and a local oscillator 107, that is, the signal frequency is increased to the carrier frequency meeting the requirements. A redundant signal generated in the frequency increasing process is filtered out through a filter 109. Finally, after the power amplifier 111 amplifies the signal to a power meeting the requirements of the frequency band of the transmitter, and the signal is then transmitted through an antenna 113.
The basic idea of the transmitter of such a structure is to complete digital signal processing at the baseband part, convert a digital signal to an analog signal through digital-to-analog conversion, and then transmit the analog signal after up conversion and power amplification.
The digital-to-analog converter (DAC) 103 is a bottleneck of the design of the transmitter. As the working frequency of the DAC is limited, a circuit such as an up converter 105 needs to be additionally provided, which increases the complexity of the design of the transmitter. A corresponding high-performance clock circuit additionally provided for the DAC not only causes a high cost of the design of the transmitter, but also increases the technical implementation complexity of hardware. The up conversion circuit and the power amplifier generate a large amount of noise signals, and particularly the noise signal generated by the local oscillator is close to a useful signal, so that a narrow band filter needs to be additionally provided for filtering, which not only increases the cost, but also makes it technically difficult to implement a wideband transmitter.
How to overcome the bottleneck of the DAC, to directly convert a baseband digital signal to a radio-frequency power signal, so as to omit circuits such as the up converter and the local oscillator, and simplify the design of the transmitter, is a research focus of the industry.
FIG. 2 is a schematic structural diagram of a digital transmitter in the prior art. For detailed introduction, see Patent Application No. WO 2008/150341. In such a transmitter structure, parallel digital radio-frequency signals are formed by N bits, from a least significant bit (Least Significant Bit, LSB) Bit 1 to a most significant bit (Most Significant Bit, MSB) Bit N. Each bit is input to one switching power amplifier 22. Output powers of all the switching power amplifiers are superimposed through a radio-frequency power combiner 24. Then, the radio-frequency signals go through a band-pass filter 25 and then sent to an antenna 27 for transmission. In such a design of the transmitter, power superimposition is performed through radio-frequency combination. The principle of the radio-frequency combination is that: for out-of-phase combination, the loss rate of the combiner is directly proportional to the number of branches, for example, for combination of 4 branches, signals to the output end are only a quarter of signals to the input end for any input port. It can be seen that, the power consumption is large, and the efficiency of the transmitter is not high.